Dielectric insulation media in liquid and/or gaseous states (i.e. fluids) are widely applied to insulate an electrically active part in a variety of electrical apparatuses, such as switchgears or transformers. For example, the electrically active part in medium or high voltage metal-encapsulated switchgears is arranged in a gas-tight compartment which encloses an insulation gas with a pressure of several bars, which electrically separates the compartment of the apparatus from the electrically active part. In other words, the insulation gas does not allow the passage of electrical current from the electrically active part to the compartment. In order to maintain the safety and functionality of the electrical apparatus, one or more operating parameters of the electrical apparatus which depend on the dielectric breakdown strength Ebd of the insulation fluid should be derived.
A commonly used dielectric insulation gas is sulfur hexafluoride (SF6) which exhibits excellent insulation and electric arc extinguishing capabilities. However, SF6 is a strong contributor to the green-house effect and thus has a high global warming potential. Therefore, alternative insulation fluids should be found. Several alternative insulation fluids have been identified. Some of these alternatives comprise multi-component fluid mixtures, i.e. they comprise more than one molecular or atomic species. Because the dielectric breakdown strength Ebd of such multi-component fluid mixtures depends, e.g., on the concentration ratio of the mixture components, its derivation becomes more complicated than for single component insulation fluids, however.
US 2002/0095262 A1 and U.S. Pat. No. 7,184,895 B2 describe methods and devices for monitoring the proportion of a component in a gaseous insulation medium consisting of at least two components.
The disclosed methods and devices have the disadvantage, however, that they do not determine the dielectric breakdown strength Ebd or an Ebd-dependent operating parameter, which is a prominent parameter relevant for assessment of an operating state of the gas-insulated electrical apparatus.